The textile and dye industries are considered to be two of the most polluting industries. While the concentration of colored components or colour contributing components in the effluent may be very small and may not be always toxic, they are a cause for substantial public apprehension due to the intense and unacceptable-colour of the effluents. Physical, chemical, biological and physico-chemical methods have been tried to treat these chromophores with various advantages and disadvantages. The approach seems to now have changed from their treatment to their removal. The factors to be considered with regard to removal by physical, chemical, biological and physico-chemical methods include cost, effectiveness, colour, need for large areas of space, ease of use, generation of concentrated sludge, large quantity of dissolved solids posing problems for its recycle or its safe disposal in the environment amongst others.
Research on novel photocatalysts using semiconductor materials (e.g., titanium dioxide) has been consistently conducted for scientific and commercial purposes. Particularly, titanium dioxide photocatalysts have been used as a means to remove pollutants causing serious environmental problems.
An article titled “Sol-gel synthesis of Au/Ti02 thin films for photo catalytic degradation of phenol in sunlight”;—in Journal of Molecular Catalysis A: Chemical 243 (2006) 68-76; by R. S. Sonawana, M. K. Dongare discloses preparation of AuATiO2 thin films used in photocatalytic decomposition of organic matter and capable of being reused repeatedly.
Photocatalytic degradation of various types of dyes such as Alizarin S, Crocein Orange G, Methyl Red, Congo Red, Methylene Blue and other organic pollutants in water by UV-irradiated titania is disclosed in an article titled “Photocatalytic degradation of various types of dyes in water by UV-irradiated titania” by Hinda Lachheb, Eric Puzenat, Ammar Houas in Applied Catalysis B: Environmental Volume 39, Issue 1, 8 Nov. 2002, Pages 75-90.
An article titled “Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: A review by Fang Han, Venkata Subba et al in applied Catalysis A: General Volume 359, Issues 1-2, 15 May 2009, Pages 25-40; discloses photocatalytic decomposition of organic pollutants and organic dyes from industrial waste water effluents involving TiO2 or modified TiO2.
An article titled “Preparation of titanium(IV) oxide thin film photo catalyst by sol-gel dip coating” in Materials Chemistry and Physics 77 (2002) 744-750 by R. S. Sonawane, S. G. Hegde, M. K. Dongare discloses TiO2 films which were used for photo catalytic decomposition of salicylic acid and methylene blue.
An article in International Journal of Photoenergy Volume 2009, Article ID 962783, 8 pages doi: 10.1155/2009/962783 titled “Nanosized TiO2 photocatalyst powder via sol-gel method: effect of hydrolysis degree on powder properties” by Nor Hafizah and lis Sopyan discloses synthesis of nanosized TiO2 powder via sol-gel method using titanium tetraisopropoxide (TPT) as the precursor in methanol for degradation of phenol and other organic pollutants.
An article titled “Photocatalytic degradation of an azo dye in a tubular continuous-flow photoreactor with immobilized TiO2 on glass plates” by Behnajady M. A. et al in Chemical engineering journal. ISSN 1385-8947, 2007, vol. 127, no1-3, pp. 167-176 discloses the photocatalytic degradation of C.I. Acid Red 27 (AR27), an anionic monoazo dye of acid class in aqueous solutions in a tubular continuous-flow photoreactor with immobilized TiO2 on glass plates. It was observed that the removal efficiency increases as the light intensity increases but it decreases when the flow rate is increased. The final outlet stream of the photoreactor showed complete mineralization of the dye.
A disadvantage associated with the use of titanium dioxide as a photocatalyst is that light of short wavelengths in the ultraviolet (UV) region is required. Also, TiO2 absorbs only 3-5% energy of the solar spectrum. For these reasons, there is a continuing need to modify pure titanium dioxide to develop photocatalytic materials capable of possessing photocatalytic activity even under visible light.
Further, molecular modification achieved in the prior art processes are complex and depend on the monomer concentration, bimolecular condensation rate and functionality that depends on the hydrolysis rate. Moreover, TiO2 is used as thin films or in polymer gel powder. The photocatalytic activity is observed to be low due to low porosity and low surface area.
Also, TiO2 films for photocatalytic decomposition of organic matter suffer from drawbacks of efficiency and versatility. The thin film comprises 100% TiO2, where the gel of the invention has been prepared with extremely low concentrations of Ti salts. Further, the Ti film is limited in its ability to treat a variety of dyes as compared to the gels of the invention exemplified herein.
Therefore there still remains a need in the art to provide a simple process for the removal of chromophores. Also, the process should be such that the treated effluent appears colorless after removal of the chromophores. Preferably, the sludge generated from the process should be easily degradable without further elaborate processes requiring time and energy resources. Further, it would definitely be advantageous if the process of the invention removes chromophores and simultaneously removes other pollutants such as phenol, methanol, formalin, hexamine and such like from the effluents, since their removal is also a challenging task to meet the environmental regulations.